Process of preparing titanium dioxide



Patented Nov. 24, 1942 UNITED STATES PATENT OFF-[CE PROCESS OF PREPARINGTITANIUM DIOXIDE Peter Tillmann, Cologne-Deutz, and Friedrich Raspe,Leverkusen-I. G. Wei-k, Germany, assignors to Titan Company, Inc.,Wilmington, Del., a corporation of Delaware No'Drawing. ApplicationNovember 14, 1939, Serial No. 304,323. In Germany November 17, 1938Claims.

The present invention relates to a process of preparing titaniumdioxide, especially TiOa pigments possessing very high tinting strength-it has special reference to the preparation of rutile titanium dioxidepigments. By rutile titanium dioxide is meant titanium dioxide havingthe crystalline structure of rutile as is distinguished from titaniumdioxide having the crystalline J. Heinen is drawn to a process ofhydrolyzing a solution of a hydrolyzable titanium salt in admixture witha nucleating sol prepared by peptizing titanium hydrate obtained from atitanium salt solution with a peptizing agent having a univalent anion.

We have now found that a sol of colloidal titanium dioxide very wellsuited for the hydrolysis of titanium salt solutions can be prepared bymixing a titanium salt having univalent anions as such or in the form ofa concentrated solution thereof, with preheated water, in such a ratiothat after the mixing the resultant sol of colloidal titanium dioxidewill have a concentration of titanium, calculated as TiOz of about 5 toabout 20g. per liter. The temperature of the water prior to the additionwith the titanium salt or I concentrated. solution thereof should besuch that after the mixing the resultant sol will have a temperature ofabout 70 C. to 100 C. When starting with titanium compounds havingunivalent anlons 'as such rather than with concentrated solutions, onaccount of the heat of dilution produced water of correspondingly lowertemperature has to be employed in order to obtain after the dilution asol having a temperature of about 70 C. to 100 C. After the admixture ofthe titanium'salt having univalent anion or a concentrated solutionthereof with the hot water, the sol obtained should preferably bemaintained at the elevated temperature for a short time in order to'stabilize the'sol and fully to develop its nucleating properties. Since bythis method dioxide is obtained which can be used immediately, thismethod of preparing the sol is specially suited for the continuoushydrolysis of titanium salt solutions.

Example Titanium tetrachlorite is diluted with such a quantity of waterthat a titanium tetrachloride solution is obtained containing 150 g. ofTiOz per liter. This titanium tetrachloride solution is added in a thinstream to water of C., while constantly stirring, in such a quantitythat'the concentration of the nuclear solution obtained,

calculated at -Ti02, amounts to 12 g. per liter. 1

This hot nuclear solution, having been kept at 85 C. for about 10 to 12minutes, is placed into the precipitation vessel, and a titanium sulfatesolution of C. containing about 190 g. T102 per liter is mixed with thenuclear solution so that the ratio by weight of titanium dioxide in thetitanium sulfate solution and titanium dioxide present as sol is to 7.5.The mixture is heated to the boil and kept boiling for 1 hour. 94 to 96%of the TiO: present in the solution are precipitated by the hydrolysis.After washing and calcining at 840 C. for one hour a rutile pigment isobtained which possesses a tinting strength of about 1600 according toReynolds method, as described on pages 92 93 of Physical and ChemicalExamination of Paints, Vamishes,

Lacquersand Colors by H. A. Gardner, 8th edition, published by theInstitute of Paint and Varnish Research. I v

We claim: a I

1. Process for the preparation of a sol of colloidal titanium dioxidehaving nucleating properties with respect to hydrolyzable titanium saltsolutions which comprises admixing a titanium salt having univalentanions with water in an amount sufiicient to yield a concentration ofti-- tanium, calculated as TiOz, between about 5 grams and about 20grams per liter, and heating to maintain a temperature between about -7QC. and 100 C. during the admixing and thereafter for a sufiicient lengthof time to produce a colloidal solution of tita'nium having a slight,stabilized opalescence and then discontinuing the heating.

2. Process for the preparation of a sol of colloidal titanium dioxidehaving nucleating properties with respect to hydrolyzable titanium saltsolutions which comprises admixing'a titanium salt having univalentanions with hot water the temperature of the water and the proportionsof water and titanium salt being such that after in one working step asol of colloidal titanium 55 the mixing the resultant colloidal solutionof titanium will have a temperature between about 70 C. and 100 C. and atitanium concentration, calculated as TiO'a, between about 5 grams and20 grams per liter, and maintaining the colloidal solution of titaniumat such temperature until a slight, stabilized opalescence is producedand then discontinuing the heating.

3. Process according to claim 2 wherein the titanium salt havingunivalent anions is used in the form of a concentrated solution.

4. Process for the hydrolytic decomposition of a hydrolyzable titaniumsalt solution which comprises admixing a titanium salt having univalentanions with water in an amount sufiicient to yield a concentration oftitanium, calculated as TiOz,

between about 5 grams and 20 grams per liter, heating to maintain atemperature between about 70 C. and 100 C. during the admixing andthereafter for a suflicient length of time to produce a colloidalsolution of titanium having a slight, stabilized opalescence, mixingsaid colloidal solution with a hydrolyzable titanium salt solution,heating the mixture hydrolytically to precipitate hydrated titaniumoxide therefrom and calcining the precipitate so obtained. 7

5. Process for the hydrolytic decomposition of a hydrolyzable titaniumsalt solution which comprises admixing a titanium salt having univalentanions with hot water the temperature of the water and the proportionsof water and titanium salt being such that after the mixing theresultant colloidal solution of titanium will have a temperature betweenabout C. and C. and a titanium concentration, calculated T103 betweenabout 5 grams and 20 grams per liter, maintaining the said colloidalsolution at such temperature until a slight, stabilized opalescence,mixing said colloidal solution with a hydrolyzable titanium saltsolution, heating the mixture hydrolytically to precipitate hydratedtitanium oxide therefrom and calcining the precipitate so obtained.

. PETER TILLMANN.

FRIEDRICH RASPE.

